Datasheet

Pin-Selectable Watchdog Timers
PIN NAME FUNCTION
1 WDI
Watchdog Input. If WDI remains either high or low for the duration of the watchdog timeout period (t
WD
), WDO
triggers a pulse. The internal watchdog timer clears whenever a WDO is asserted or whenever WDI sees a
rising or falling edge.
2 GND Ground
3 N.C. Not Connected. Do not make any connection to this pin.
4 SET0 S et Z er o. Log i c i np ut for sel ecti ng star tup d el ay and w atchd og ti m eout p er i od s. S ee Tab l e 1 for ti m i ng d etai l s.
5 SET1 S et One. Log i c i np ut for sel ecti ng star tup d el ay and w atchd og ti m eout p er i od s. S ee Tab l e 1 for ti m i ng d etai l s.
6 SET2 S et Tw o. Log i c i np ut for sel ecti ng star tup d el ay and w atchd og ti m eout p er i od s. S ee Tab l e 1 for ti m i ng d etai l s.
7 WDO
Watchdog Output. Pulses low for the watchdog output pulse width, t
WDO
, when the internal watchdog times
out. The MAX6369/MAX6371/MAX6373 have open-drain outputs and require a pull-up resistor. The
MAX6370/MAX6372/MAX6374 outputs are push-pull.
8V
CC
Supply Voltage (+2.5V to +5.5V)
Table 1. Minimum Timeout Settings
Pin Description
Detailed Description
The MAX6369–MAX6374 are flexible watchdog circuits
for monitoring µP activity. During normal operation, the
internal timer is cleared each time the µP toggles the
WDI with a valid logic transition (low to high or high to
low) within the selected timeout period (t
WD
). The WDO
remains high as long as the input is strobed within the
selected timeout period. If the input is not strobed
before the timeout period expires, the watchdog output
is asserted low for the watchdog output pulse width
(t
W
DO
). The device type and the state of the three logic
control pins (SET0, SET1, and SET2) determine watch-
dog timing characteristics. The three basic timing varia-
tions for the watchdog startup delay and the normal
watchdog timeout period are summarized below (see
Table 1 for the timeout characteristics for all devices in
the family):
• Watchdog Startup Delay:
Provides an initial delay before the watchdog timer is
started.
Allows time for the µP system to power up and initial-
ize before assuming responsibility for normal watch-
dog timer updates.
Includes several fixed or pin-selectable startup delay
options from 200µs to 60s, and an option to wait for
the first watchdog input transition before starting the
watchdog timer.
LOGIC INPUTS MAX6369/MAX6370 MAX6371/MAX6372 MAX6373/MAX6374
SET2 SET1 SET0 t
DELAY
, t
WD
t
DELAY
= 60s, t
WD
t
DELAY
t
WD
0 0 0 1ms 1ms 3ms 3ms
0 0 1 10ms 3ms 3s 3s
0 1 0 30ms 10ms 60s 1s
0 1 1 Disabled Disabled Disabled Disabled
1 0 0 100ms 100ms 200μs30μs
1 0 1 1s 300ms First Edge 1s
1 1 0 10s 3s First Edge 10s
1 1 1 60s 60s 60s 10s
Maxim Integrated
5
MAX6369–MAX6374